Changes in pressure influences are experienced in many fluid systems. For various installations such pressure changes may be desired or undesirable depending on uses of the individual systems. Whether the pressure changes are purposely induced or not, it is often desirable to have a signal output indicating the occurrence of such pressure changes. Control systems, position indicating and other devices can be provided of a signal indication is available to indicate the occurrence of fluid pulse, changes in differential pressure or other similar changes in the system operation. Since electrical instrumentation and control components are extensively available, it is desirable to provide an electrical signal output that is responsive to changes in fluid pressures. Various air switches that may be diaphragm or piston operated have previously been used and devised to satisfy user requirements. The most extensive previous development has been in fields providing devices that are sensitive to larger pressure differentials, but it is further acknowledged that extensive development has also been accomplished in low pressure pneumatic systems where the flow of air may be used for control, counting or logic purposes.
The present inventors have previously been concerned with the provision and use of an air switch type device in automatic pinsetter bowling machines. One such device is shown in U.S. Pat. No. 3,790,167 by the same inventors. In the mentioned patent disclosure a diaphragm operated type of air switch is used together with time delay components to actuate pinsetter, bowling scorer and other components. User experiences with diaphragm type switches indicate that improved sensitivity and reliability features are desirable for use in the field of low pressure electric switch or signal output apparatus.